1. Field of the Invention
The present invention relates to a coupling structure of optical fibers and optical waveguides which is used in an optical communication system as an optical waveguide module having an optical waveguide circuit.
2. Related Background Art
In the field of optical communications, for the purpose of, e.g., processing signals from optical fibers by optical waveguides, a coupling structure in which the optical fibers and the optical waveguides are optically coupled is sometimes needed.
For example, in a conventional coupling structure in which optical fibers and optical waveguides are coupled by welding, an optical fiber arranging connector in which a multi optical fiber extending from a ribbon fiber is arranged, and a waveguide substrate on which an optical waveguide layer including a multi optical waveguide is formed, are fixed in separate metal members. The end faces of the optical fiber arranging connector and the waveguide substrate respectively fixed in the metal members are abutted against each other, and the optical fibers and the optical waveguides are aligned with each other. Then, the metal members are welded with each other by using, e.g., a YAG laser.
In the above coupling structure, however, since the metal members are deformed during welding, the optical waveguides and the optical fibers cause misalignment to increase the light transmission loss of the coupling structure. Since the metal members are used as metal housings of the optical fiber arranging connector and the optical waveguide layer, the manufacturing cost becomes very high. Thus, a demand has arisen for a coupling structure of optical fibers and optical waveguides free from these problems.
In a conventional coupling structure in which optical fibers and optical waveguides are coupled by using a photo-setting (photo-curable) adhesive, a multi optical fiber extending from a ribbon fiber is arranged by being fixed in, e.g., the V-grooves of a glass optical fiber arranging connector. A waveguide substrate on which an optical waveguide layer including a multi optical waveguide is formed is mounted in a glass member, and the optical fibers and the optical waveguides are aligned with each other. A photo-setting adhesive is injected between the end faces of the optical fiber arranging connector and the glass member to be coupled, and light is radiated from the peripheral portion, thereby setting the photo-setting adhesive. In order to sufficiently set the photo-setting adhesive, as described above, the optical fiber arranging connector is made of a glass material (e.g., quartz glass) which transmits light having a wavelength capable of setting the adhesive (e.g., an ultraviolet-curing resin) at a high transmittance.
In the above coupling structure, the optical fiber arranging connector is connected to one or two ends, i.e., one or both of the input and output portions, of the waveguide substrate.
A prior art technique concerning the coupling structure of optical fibers and optical waveguides in which an optical fiber arranging connector and a waveguide substrate are adhered by using a photo-setting adhesive is described in, e.g., "IEEE Photonics Technology Letters, Vol. 4, No. 8, pp. 906-908, August 1992" in detail. A prior art technique concerning the coupling structure of optical fibers and optical waveguides in which an optical fiber arranging connector and a waveguide substrate are mechanically fixed is described in, e.g., "Ceramics 29, No. 4, pp. 319-321, 1994" in detail.
A prior art technique concerning the coupling structure of optical fibers and optical waveguides in which optical fibers are directly fitted in a processed waveguide substrate is described in, e.g., Japanese Patent Laid-Open No. 63-279206 (French Patent No. 8,703,385, Mar. 12, 1987), Japanese Patent Laid-Open No. 1-186905 (French Patent No. 8,716,398, Nov. 26, 1987), and International Patent Laid-Open No. 4-507153 (French Patent No. 9,002,575, Mar. 1, 1990) in detail.
A prior art technique concerning the coupling structure of optical fibers and optical waveguides in which quartz glass housings respectively incorporating a waveguide substrate and an optical fiber arranging connector are welded with each other by heating is described in, e.g., Japanese Patent Laid-Open No. 2-253206 in detail. A prior art technique concerning the coupling structure of optical fibers and optical waveguides in which optical fibers are directly adhered to a waveguide substrate is described in, e.g., Japanese Patent Laid-Open No. 5-173039 (U.S. Pat. No. 5,185,835, Feb. 9, 1993) in detail.